1. Field of the Invention
The present invention relates to a rotary power tool, more particularly to a rotary power tool having a multiple speed transmission for providing at least three gear speed ratios.
2. Background Art
Rotary power tools are well known in the art and offer various operational features for allowing a user to operate a tool in a desired manner. For example, electric drills offer a wide variety of features to achieve such objectives. In the advent of cordless or battery operated power tools, more flexibility is provided to the user and various benefits are achieved including light weight, compactness, costs and others.
Cordless drills are generally low in torque and high in speed in comparison to conventional corded drills and have allowed manufacturers to use planetary gear sets rather than spur gears, as commonly utilized in the conventional corded drills. Planetary gear sets have allowed manufacturers and consumers to appreciate the benefits provided by planetary gear sets including a relatively low cost, compactness and a lightweight gear box. Utilization of planetary gear sets has further allowed the use of molded, polymeric or fiberglass reinforced polymeric gear sets offering suitable strength characteristics to translate an output torque, while being relatively light in weight.
Advancements in the cordless power tool art resulted in the utilization of adjustable clutches incorporated in the power tool between the transmission and an output tool holder for adjusting the torque output and preventing an overloading upon the motor. An examplary torque output device is disclosed in U.S. Pat. No. 5,277,527, issued on Jan. 11, 1994 to Ryobi Limited, and incorporated by reference herein. Another feature that has been provided to cordless drills is the incorporation of a multiple speed transmission, thus allowing a user to select a preferred output speed for the rotary operation. Multiple speed transmissions have existed in the art of corded drills, however they typically utilized multiple spur gears, thus adding to weight and size of the tool.
The prior art teaches various methods for providing multiple or variable speed rotary power tools. For example, U.S. Pat. No. 4,791,833, issued to Sakai et al., on Dec. 20, 1988, teaches a rotary power tool having a two-speed planetary gear set transmission wherein a ring gear is shiftable for either two-stage or three-stage gear reduction.
Accordingly, three-speed gear boxes have been utilized in the prior art for offering a wider range of speed selection to the user. For example, U.S. Pat. No. 4,418,766, issued to Grossman on Dec. 6, 1983, discloses a compact three speed gear box utilizing a plurality of spur gears for providing three output speeds from a corded drill. Bosch incorporated a similar design in a cordless drill, GBM 12 VES-3. Another three-speed gear box is disclosed in U.S. Pat. No. 6,431,289 B1, issued to Potter et al., on Aug. 13, 2002. The Potter ""289 patent utilizes a pair of axially translatable ring gears within a multiple stage transmission having planetary gear sets for allowing at least three multiple gear speed ratios.
Another three-speed power tool is disclosed in U.S. Patent Application Publication No. 2002/0049111 Al. This reference teaches three planetary gear sets, all having a common input member and a common planet carrier. A shiftable sleeve selectively engages a ring gear of each planetary gear set for providing multiple gear speed reduction ratios.
With the benefits of cost, compactness, weight, and multiple speed output in consideration, the prior art teaches the utilization of either multiple actuation members, or an actuation member for engaging at least three gear stages in order to provide three or more gear speed ratios. Accordingly, a cordless power tool having a shift actuator for engaging at least two gear sets to provide at least three speeds of gear reduction is needed.
An object of the invention is to provide a portable electric rotary power tool having a multiple speed transmission. The power tool includes an electric motor oriented within a housing. The motor has a rotary output shaft for providing a first output torque. A plurality of gear reduction elements are included in the power tool, for receiving the first output torque and driving an output spindle. At least two of the gear reduction elements have a common input member and a common output member, and the at least two gear reduction elements each have a locked mode, a reduction mode, and a disengaged mode. A shift actuator is in selective communication with the two gear reduction elements, and has a first position wherein the two gear reduction elements are each in the locked mode for providing the first output torque to the spindle. The shift actuator has a second position wherein the first of the two gear reduction elements is in the reduction mode and the other is in the disengaged mode for providing a second output torque to the spindle. The shift actuator also has a third position wherein the first is in the disengaged mode and the other is in the reduction mode for providing a third output torque to the spindle.
A further aspect of the invention defines the two gear reduction elements as planetary gear sets, each including a sun gear, a plurality of planet gears oriented about and engaged with the sun gear, a planet carrier, to which each of the planet gears is fixed for rotation, and a ring gear oriented about and engaged with the plurality of planet gears.
According to another aspect of the invention, the shift actuator is an axially translatable sleeve wherein, in the first position, the shift actuator engages the planet carrier and ring gear of the first planetary gear set for locking the first and second planetary gear sets relative to the common input member in the locked mode so that the first output torque is transmitted to the spindle. In the second position, the shift actuator engages the ring gear of the first planetary gear set and the housing for securing the ring gear of the first planetary gear set relative to the housing, so that the first output torque is received by the first planetary gear set in the reduction mode and the second planetary gear set is in the disengaged mode so that the second output torque is transmitted to the common output member. In the third position, the shift actuator engages the ring gear of the second planetary gear set and the housing for securing the ring gear of the second planetary gear set relative to the housing in the reduction mode and the first planetary gear set is in the disengaged mode so that the first output torque is received by the second planetary gear set and the third output torque is transmitted to the spindle.
Yet another aspect of the invention defines the first and second planetary gear sets as having a common input member wherein the respective sun gears are fixed relative to one another, and wherein the common output member is a common planet carrier for both the first and second planetary gear sets. The shift actuator is further defined as an axially translatable common input member or an axially translatable planet carrier for providing the three positions resulting in the three multiple gear speed reduction ratios.